Ignition system for internal combustion engines

ABSTRACT

An ignition system for internal combustion engines with sequential spark ignition is provided which serves to ensure that the last individual spark (EZ) of a sequential spark ignition does not lead to damage to the internal combustion engine, for instance damage caused by ignition during the exhaust stroke. A closing time corresponding to a charging process (AL) for an individual ignition is subtracted from a distribution limit (VG) to obtain a calculated limit (11). Once this limit is reached, the current charging process proceeds unimpeded to trigger the individual ignition, but no new charging process will be started.

BACKGROUND OF THE INVENTION

An ignition system for internal combustion engines for the production ofsequential spark ignitions is known from Federal Republic of GermanyPatent 23 40 865. A sequential spark ignition is an ignition at thedesired firing time calculated by the control device but the sparks ofwhich, are not allowed to burn out entirely. Instead, the coil isrecharged utilizing the residual energy and ignites again.

This process is repeated until the distribution limit is reached. Thedistribution limit is the crankshaft angle which a firing time of thelast ignition of a sequential spark ignition must not exceed. If thedistribution limit is exceeded, then there is a danger that, with thehigh voltage distribution at rest, the ignition spark may fall withinthe exhaust stroke, or that, with rotating voltage distribution, thehigh voltage available may be imparted to the spark plug of the nextcylinder. In both cases this would have a negative influence on thetravel behavior of the internal combustion engine. Therefore, until now,the charging process of the last individual ignition of a sequentialspark ignition has been interrupted upon reaching the distributionlimit.

SUMMARY OF THE INVENTION

In accordance with the present invention, in addition to thedistribution limit, a further crankshaft angle is introduced which isobtained by subtracting the closing angle corresponding to a chargingprocess of an individual ignition from the angle of the distributionlimit. In this way, the charging process of the last individual ignitionof the sequential spark ignition can, in all cases, be completed so thatthe energy stored is sufficient for the triggering of an ignition spark.As a result, the starting of a charging process which would beinterrupted upon reaching the distribution limit regardless of how fullthe coil was charged is avoided. This means that no unnecessary lossesof energy occur. At the same time, since the primary current in theignition coil is detected, a disconnecting of the primary current takesplace only when the energy stored is sufficient to produce an ignitionspark under normal conditions. The control device of the internalcombustion engine can continue, by detection of the supply voltage, toadapt the closing time of each individual ignition of the sequentialspark ignition in accordance with the conditions of the internalcombustion engine, so that a disconnection of the primary current iseffected only when the energy stored in the ignition coil produces anignition spark on the spark plug under normal operating conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the construction in principle of an ignition system;

FIG. 2 shows the charging processes of the individual ignitions of asequential spark ignition plotted over the corresponding time range orthe range of the crankshaft angle within which the sequential sparkignition takes place; and

FIG. 3(a-c) shows the charging processes of the individual ignitionswith different supply voltage.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an ignition system of an internal combustion engine. Acontrol device 1, for instance a microprocessor, detects variousoperating parameters of the internal combustion engine, such as speed ofrotation n, pressure p, supply voltage U_(B), temperature T, etc. asinput variables 2 in order to determine the ignition time ZZP. Via aconnection 3 of the control device 1, the ignition transistor 4 isactuated for the connecting and disconnecting of the flow of current inthe ignition coil 5. The ignition transistor 4 is connected on thecollector side to the supply voltage U_(B) via a series connection withthe primary winding 6. On the emitter side, the ignition transistor 4 isconnected to ground via a current shunt 7. Between the emitter of theignition transistor and the current shunt 7, there is a tap 8 fromwhich, via a connection 9 in the control device 1, a voltage which isproportional to the primary current I_(p) is detected during the drivingof the control transistor 4.

FIG. 2 shows the variation with time of the primary current I_(p) duringthe individual ignitions EZ of a sequential spark ignition FZZ over therange of the crankshaft angle within which the sequential spark ignitionis triggered. The course of the primary current is also shown, over thetime t, with respect to the top dead center OT. After reaching thefiring time ZZP, for instance 10° crankshaft angle before top deadcenter (OT), the first individual ignition EZ1 is triggered by thecontrol device. In this connection it is possible, by the detection ofthe primary current I_(p) in the control device, to trigger the ignitiononly when a predeterminable maximum value I_(max) has been reached. Inthis way, the energy stored in the ignition coil is guaranteed to besufficient under normal operating conditions for an ignition spark.After interruption of the charging process AL of the first individualignition EZ1, the ignition spark burns until the reconnection of theignition coil current for the second individual ignition EZ2. Thisprocess is repeated four times in the embodiment shown, so that thesequential spark ignition FFZ is formed for four individual ignitionsEZ1 to EZ4.

On the crankshaft-angle or time axis there is illustrated thedistribution limit VG at which the sequential spark ignition FFZ isinterrupted in order to prevent destruction of the ignition system. Thedistribution limit VG in the embodiment of FIG. 2 lies at 18° crankshaftangle after top dead center OT. The dashed line 10 indicates thecharging process AL of the last individual spark ignition. In thisconnection, it can be clearly noted that the charging process AL is notsufficient to reach a predetermined value of the primary current I_(max)so that an ignition spark is produced under normal operating conditions.The charging process of an individual ignition is, for instance,dependent on the parameters of the ignition coil or the instantaneousoperating conditions. The charging process of the first individualignition is in this case about 5 ms and the charging process of thefollowing individual ignitions AL1 is 2 ms. The charging process of thefirst individual ignition EZ1 of a sequential spark ignition FFZ islonger than the charging process AL of the following individualignitions. This is due to the fact that, upon the charging process ofthe first individual ignition EZ1, under normal conditions no residualenergy is present in the ignition coil, while in the case of thefollowing individual ignitions the ignition spark does not burn outcompletely by the reconnecting of the ignition coil and thus residualenergy is still stored in the ignition coil. Therefore, in accordancewith the present invention in addition to the distribution limit VG,another limit value 11 is introduced, which is determined by subtractinga charging process AL from the distribution limit VG. A charging processat the coil which has already been introduced at 11 is still brought toan end and still ignited. However, if no charging has started, i.e. theadditional limit 11 coincides with the open time, which amounts forinstance to 15 μs, no charging and therefore no individual ignition EZis started. As a result, the last individual ignition EZ of a sequentialspark ignition FFZ is carried out with the maximum possible sparkenergy--in the example shown in FIG. 2, this is the individual ignitionEZ4.

The rise of the primary current I_(p) and thus the energy stored in theignition coil is dependent on the parameters of the ignition coil andalso on the supply voltage U_(B). Therefore, the supply voltage U_(B) isalso to be taken into consideration in the determination of the durationof the charging process AL.

FIGS. 3a, 3b and 3c show the course of the primary current I_(p) forindividual ignitions EZ as a function of the supply voltage U_(B), thecourse of the primary current in the case of a high supply voltage U_(B)(large) being shown in FIG. 3a, course in the case of medium supplyU_(B) (medium) in FIG. 3b, and the course of a small supply voltageU_(B) (small) in FIG. 3c. The rise of the primary current I_(p) with thesame supply voltage U_(B) is the same for all charging processes AL withthis supply voltage.

Each of FIGS. 3a to 3c shows the course of the primary current of, ineach case, three individual ignitions. In this connection it can benoted that in the case of the individual ignitions of FIG. 3a, andtherefore with large supply voltage U_(B) (large), a predeterminablemaximum value of the primary current I_(max) is reached within a shortertime t than predetermined (AL) than in the case of the individualignitions of FIG. 3b, while the maximum value I_(max) of the primarycurrent I_(p) in the case of too low a supply voltage U_(B) (small)is--as can be noted from FIG. 3c--not reached at all with fixedpredetermined charging time A1. The second individual ignition of FIG.3a shows that the primary current I_(p) has already reached the maximumvalue I_(max) for an ignition under normal operating conditions beforethe end of the charging process AL. In order to avoid unnecessarylosses, an interruption of the charging process could be brought aboutby the control device already upon the reaching of the maximum valueI_(max), and therefore at I_(p) =I_(max). Thus, for instance, the thirdindividual ignition in FIG. 3c shows a shortened charging process.

In order to exclude the above deficiencies, the supply voltage is ineach case detected by the control device 1 and a correspondingly adaptedcharging time calculated for the individual ignition.

What is claimed is:
 1. An ignition system for an internal combustionengine, comprising:a control device for controlling a flow of current inat least one ignition coil; the control device repeatedly connecting anddisconnecting a primary current from the at least one ignition coil tospark a plurality of individual ignitions of a sequential sparkignition, wherein each connection of the primary current to the at leastone ignition coil signifies a starting of a charging process for acorresponding one of the plurality of individual ignitions and eachdisconnection of the primary current from the at least one ignition coilsignifies a closing of the charging process for the corresponding one ofthe plurality of individual ignitions, a charging process time for thecorresponding one of the plurality of individual ignitions being adifference between a time of the closing of the charging process for thecorresponding one of the plurality of individual ignitions and a time ofthe starting of the charging process for the corresponding one of theplurality of individual ignitions; and the control device determining adistribution limit and determining a charging process time for a finalignition of the plurality of individual ignitions, the control devicesubtracting the charging process time for the final ignition of theplurality of individual ignitions from the distribution limit to obtainanother limit, the control device inhibiting the starting of thecharging process for any one of the plurality of individual ignitionsafter the another limit is reached.
 2. The ignition system according toclaim 1, wherein the ignition system is for an internal combustionengine with a rotating distribution, and wherein the distribution limitcorresponds to a crankshaft angle, the crankshaft angle corresponding toa possible ignition spark in a next cylinder in a sequence of theplurality of individual ignitions.
 3. The ignition system according toclaim 1, wherein the ignition system is for an internal combustionengine with a stationary distribution, and wherein the distributionlimit corresponds to a crankshaft angle, the crankshaft anglecorresponding to an exhaust stroke of a possible ignition spark in apresent cylinder in a sequence of the plurality of individual ignitions.4. The ignition system according to claim 1, further comprising ameasuring device coupled to the control device for measuring the primarycurrent in the at least one ignition coil, the control deviceinterrupting the charging process of a corresponding one of theplurality of individual ignitions when the measured primary currentreaches a predetermined reference value.
 5. The ignition systemaccording to claim 1, wherein the control device determines the closingtime of the charging process for each individual ignition as a functionof a supply voltage, wherein the closing time of the charging processfor each individual ignition is inversely proportional to the supplyvoltage.
 6. A method for controlling ignition in an internal combustionengine, comprising the steps of:controlling a flow of current in atleast one ignition coil by repeatedly connecting and disconnecting aprimary current from the at least one ignition coil to spark a pluralityof individual ignitions of a sequential spark ignition, wherein eachconnection of the primary current to the at least one ignition coilsignifies a starting of a charging process for a corresponding one ofthe plurality of individual ignitions and each disconnection of theprimary current from the at least one ignition coil signifies a closingof the charging process for the corresponding one of the plurality ofindividual ignitions, a charging process time for the corresponding oneof the plurality of individual ignitions being a difference between atime of the closing of the charging process for the corresponding one ofthe plurality of individual ignitions and a time of the starting of thecharging process for the corresponding one of the plurality ofindividual ignitions; determining a distribution limit; determining acharging process time for a final ignition of the plurality ofindividual ignitions; subtracting the charging process time for thefinal ignition of the plurality of individual ignitions from thedistribution limit to obtain another limit; and inhibiting the startingof the charging process for any one of the plurality of individualignitions after the another limit is reached.
 7. The method according toclaim 6, wherein the ignition system is for an internal combustionengine with a rotating distribution, and wherein the distribution limitcorresponds to a crankshaft angle, the crankshaft angle corresponding toa possible ignition spark in a next cylinder in a sequence of theplurality of individual ignitions.
 8. The method according to claim 6,wherein the ignition system is for an internal combustion engine with astationary distribution, and wherein the distribution limit correspondsto a crankshaft angle, the crankshaft angle corresponding to a possibleignition spark in an exhaust stroke of a present cylinder in a sequenceof the plurality of individual ignitions.
 9. The method according toclaim 6, further including the steps of:measuring the primary current inthe at least one ignition coil; and interrupting the charging process ofa corresponding one of the plurality of individual ignitions when themeasured primary current reaches a predetermined reference value. 10.The method according to claim 6, wherein the determining step furtherincludes determining the closing time of the charging process for eachindividual ignition as a function of a supply voltage, wherein theclosing time of the charging process for each individual ignition isinversely proportional to the supply voltage.